.TH std::multimap 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::multimap \- std::multimap

.SH Synopsis
   Defined in header <map>
   template<

       class Key,
       class T,                                                       \fB(1)\fP
       class Compare = std::less<Key>,
       class Allocator = std::allocator<std::pair<const Key, T>>

   > class multimap;
   namespace pmr {

       template<
           class Key,
           class T,                                                   \fB(2)\fP \fI(since C++17)\fP
           class Compare = std::less<Key>
       > using multimap = std::multimap<Key, T, Compare,
           std::pmr::polymorphic_allocator<std::pair<const Key, T>>>;

   }

   std::multimap is an associative container that contains a sorted list of key-value
   pairs, while permitting multiple entries with the same key. Sorting is done
   according to the comparison function Compare, applied to the keys. Search,
   insertion, and removal operations have logarithmic complexity.

   Iterators of std::multimap iterate in non-descending order of keys, where
   non-descending is defined by the comparison that was used for construction. That is,
   given

     * m, a std::multimap
     * it_l and it_r, dereferenceable iterators to m, with it_l < it_r.

   m.value_comp()(*it_r, *it_l) == false (least to greatest if using the default
   comparison).

   The order of the key-value pairs whose keys compare equivalent is the  \fI(since C++11)\fP
   order of insertion and does not change.

   Everywhere the standard library uses the Compare requirements, equivalence is
   determined by using the equivalence relation as described on Compare. In imprecise
   terms, two objects a and b are considered equivalent if neither compares less than
   the other: !comp(a, b) && !comp(b, a).

   std::multimap meets the requirements of Container, AllocatorAwareContainer,
   AssociativeContainer and ReversibleContainer.

.SH Template parameters

    This section is incomplete
    Reason: Add descriptions of the template parameters.

.SH Member types

   Member type             Definition
   key_type                Key
   mapped_type             T
   value_type              std::pair<const Key, T>
   size_type               Unsigned integer type (usually std::size_t)
   difference_type         Signed integer type (usually std::ptrdiff_t)
   key_compare             Compare
   allocator_type          Allocator
   reference               value_type&
   const_reference         const value_type&
                           Allocator::pointer                        \fI(until C++11)\fP
   pointer                 std::allocator_traits<Allocator>::pointer \fI(since C++11)\fP


                           Allocator::const_pointer                        (until
                                                                           C++11)
   const_pointer           std::allocator_traits<Allocator>::const_pointer (since
                                                                           C++11)


   iterator                LegacyBidirectionalIterator to value_type
   const_iterator          LegacyBidirectionalIterator to const value_type
   reverse_iterator        std::reverse_iterator<iterator>
   const_reverse_iterator  std::reverse_iterator<const_iterator>
   node_type \fI(since C++17)\fP a specialization of node handle representing a container
                           node

.SH Member classes

   value_compare compares objects of type value_type
                 \fI(class)\fP

.SH Member functions

   constructor   constructs the multimap
                 \fI(public member function)\fP
   destructor    destructs the multimap
                 \fI(public member function)\fP
   operator=     assigns values to the container
                 \fI(public member function)\fP
   get_allocator returns the associated allocator
                 \fI(public member function)\fP
.SH Iterators
   begin         returns an iterator to the beginning
   cbegin        \fI(public member function)\fP
   \fI(C++11)\fP
   end           returns an iterator to the end
   cend          \fI(public member function)\fP
   \fI(C++11)\fP
   rbegin        returns a reverse iterator to the beginning
   crbegin       \fI(public member function)\fP
   \fI(C++11)\fP
   rend          returns a reverse iterator to the end
   crend         \fI(public member function)\fP
   \fI(C++11)\fP
.SH Capacity
   empty         checks whether the container is empty
                 \fI(public member function)\fP
   size          returns the number of elements
                 \fI(public member function)\fP
   max_size      returns the maximum possible number of elements
                 \fI(public member function)\fP
.SH Modifiers
   clear         clears the contents
                 \fI(public member function)\fP
                 inserts elements
   insert        or nodes
                 \fI(since C++17)\fP
                 \fI(public member function)\fP
   insert_range  inserts a range of elements
   (C++23)       \fI(public member function)\fP
   emplace       constructs element in-place
   \fI(C++11)\fP       \fI(public member function)\fP
   emplace_hint  constructs elements in-place using a hint
   \fI(C++11)\fP       \fI(public member function)\fP
   erase         erases elements
                 \fI(public member function)\fP
   swap          swaps the contents
                 \fI(public member function)\fP
   extract       extracts nodes from the container
   \fI(C++17)\fP       \fI(public member function)\fP
   merge         splices nodes from another container
   \fI(C++17)\fP       \fI(public member function)\fP
.SH Lookup
   count         returns the number of elements matching specific key
                 \fI(public member function)\fP
   find          finds element with specific key
                 \fI(public member function)\fP
   contains      checks if the container contains element with specific key
   (C++20)       \fI(public member function)\fP
   equal_range   returns range of elements matching a specific key
                 \fI(public member function)\fP
   lower_bound   returns an iterator to the first element not less than the given key
                 \fI(public member function)\fP
   upper_bound   returns an iterator to the first element greater than the given key
                 \fI(public member function)\fP
.SH Observers
   key_comp      returns the function that compares keys
                 \fI(public member function)\fP
   value_comp    returns the function that compares keys in objects of type value_type
                 \fI(public member function)\fP

.SH Non-member functions

   operator==
   operator!=
   operator<
   operator<=
   operator>
   operator>=               lexicographically compares the values of two multimaps
   operator<=>              \fI(function template)\fP
   (removed in C++20)
   (removed in C++20)
   (removed in C++20)
   (removed in C++20)
   (removed in C++20)
   (C++20)
   std::swap(std::multimap) specializes the std::swap algorithm
                            \fI(function template)\fP
   erase_if(std::multimap)  erases all elements satisfying specific criteria
   (C++20)                  \fI(function template)\fP

     Deduction guides \fI(since C++17)\fP

.SH Notes

       Feature-test macro       Value    Std                   Feature
   __cpp_lib_containers_ranges 202202L (C++23) Ranges construction and insertion for
                                               containers

.SH Example

    This section is incomplete
    Reason: no example

   Defect reports

   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.

     DR    Applied to           Behavior as published              Correct behavior
                      Key was not required to be
   LWG 230 C++98      CopyConstructible                         Key is also required to
                      (a key of type Key might not be able to   be CopyConstructible
                      be constructed)

.SH Categories:
     * Todo with reason
     * Todo no example
